The authors det. structural and electronic properties of NanMg clusters using the Car-Parrinello method. The low-energy isomers, which result from a dynamical simulated annealing search, can be described as substitutionally doped Na clusters. The Mg impurity is never located at the center of the cluster, in contrast to the assumptions of spherical jellium models (SJMs) and of earlier ab initio calcns. Accordingly, the electronic configuration is found to be more complex than that predicted by SJMs. The exptl. obsd. disappearance of a magic no. at n = 8 on passing from NanZn and KnMg to NanMg is explained as a result of the difference in the low-energy structures. [on SciFinder (R)]